In today's market, polyurethane coated fabrics are utilized in a wide array of products and applications, including producing high performance coated fabrics for severe use applications.
Typically, polyurethane elastomers which are considered top of the line with respect to performance, include, for example, polytetramethylene glycol (polyether) polyurethanes and poly(butane adipates or hexane adipates) ester polyurethanes. Of these polymers, the polyether polyurethanes exhibit good hydrolytic stability and low temperature properties but are generally poor for fuel resistance and oxidation resistance, while the polyester polyurethanes are tough with good abrasion resistance, oxidation resistance and fuel resistance, but not particularly resistant to hydrolysis. Still, at the present time the polyesters are generally considered to represent the best compromise of physical properties and chemical resistance of the various polyurethanes.
There are also a few polyurethanes based on polycarbonate polyols in the market. It is well known that these polycarbonate polyurethanes have very good hydrolytic stability and generally have good to very good resistance to other degradation forces; however, these polyurethanes are usually too hard, rigid and brittle for use in industrial coated fabrics.
Currently, high performance coated fabrics are based on polyester polyurethanes in order to meet the specifications currently in effect, but resistance to hydrolysis remains as a weak point and represents a problem for these products Thus, there is a desire for improved hydrolytic stability in a number of applications. A polyurethane having improved hydrolytic properties and sufficient elastomeric character to be useful in the manufacturing of industrial coated fabrics is also desirable and needed
In addition, the construction of the fabric reinforcement is important for increasing the strength of the coated fabric. The combination of a high performance polyurethane coating and fabric reinforcement is required to provide a product which is useful for severe use applications. One such application is disclosed in U.S. Pat. No. 3,834,200 to Winter In this patent, a polyurethane impregnated nylon scrim was found to have the desired combination of flexibility, resiliency, toughness and tear resistance for use as a peening flap. As the operational characteristics of such peening devices has been increased, the specific coated fabric disclosed therein, Reevecoat 7625, a conventional polyester polyurethane coated fabric, did not have sufficient mechanical properties to provide a useful service life. Thus, a new coated fabric with improved properties was needed to withstand the improved operational characteristics of the new peening device.
Another severe use application of polyurethane coated fabrics is fuel cell fabrication in the aviation fuel containment field. In a fuel cell, there is provided an inner layer an outer layer and a fuel barrier layer located between the inner and outer layer of the fuel cell. Sometimes, there is also provided a reinforcing or crashworthy layer located between the outer layer and the fuel barrier layer. This crash worthy layer is utilized to retain fuel in the cell in the event of a crash landing. In these fuel cells, polyurethane coated fabrics have been utilized as the inner and/or outer layers, as well as for the crash worthy layer. Again, as technology advances, greater demands are made on these materials in that higher performance is needed in a lighter weight coated fabric.
The performance of these products in a severe use environment is limited by the coated fabric utilized in their manufacture. There is a need for a coated fabric that possess good abrasion resistance, toughness, strength, chemical resistance, flexibility and resiliency for use in such applications. There is also a need for a coated fabric that provides a longer useful life in such applications to keep pace with advances in the devices in which they are used to improve the operation or economy of such devices.